Typically employed DNA synthesis procedures for scalable DNA construction have the following disadvantages: (a) high cost of oligonucleotides, (b) low assembly efficiency into long DNA sequences, (c) time-consuming cloning, and (d) high cost of target DNA sequence validation. Above all, the major synthesis costs are the costs of oligonucleotides and sequencing. It would thus be desirable to design a protocol for massively parallelizing synthesis products in order to achieve effective, highly scalable DNA synthesis. DNA oligonucleotides derived from DNA microchips have previously been utilized to synthesize scalable low-cost DNA (Tian, J., et al., 2004). However, the low assembly efficiency of chip-derived oligonucleotides hinders target gene construction, and a laborious DNA assembly optimization process is consequently required. The inefficiency of DNA assembly from chip-derived oligonucleotides is largely associated with the incomplete removal of flanking regions of double-stranded (ds)-oligonucleotides prior to their assembly and the uneven concentration of each chip-cleaved oligonucleotide (Kim H., et al., 2011). Furthermore, it was observed that a greater number of oligonucleotides (i.e. higher complexity) in a DNA assembly pool made DNA assembly less efficient (Kim H., et al., 2011; Borovkov A. Y., et al., 2010). As a consequence, only a small sub-pool of oligonucleotides (i.e. <20) are often amplified to ensure high assembly efficiency. There is a need to develop a high-efficiency DNA assembly process using a large number of microchip oligonucleotides present in a pool in order to attain all advantages of ultra-low cost DNA microchip oligonucleotides.
For scalable DNA synthesis, it is preferable to decrease the sequencing cost for target DNA validation. In recent years, costs for high-throughput sequencing technologies have been considerably lowered. Under such circumstances, utilization of high-throughput sequencing technology has great potential for DNA synthesis at ultra-low cost. However, unlike colony-based Sanger sequencing validation, it is difficult to collect the desired DNA from a pool of high-throughput sequenced DNA mixtures. Although recent high-throughput sequencing technologies can be applied to partially addressable spots (for example, clonal spots available from Roche-454, Illumina and SOLiD, and single-molecule spots available from Helicos and PacBio), it is difficult to isolate target DNA due to the difficulty associated with the collection of the desired DNA from high-throughput sequencing plates. In a notable report (Matzas M., et al., 2010), chip-cleaved oligonucleotides were sequenced by 454 sequencing technology, and directly isolated from the 454 sequencing plate using a bead picker pipette. These sequence-validated ‘oligonucleotides’ were subsequently processed and used to assemble 200 bp target DNA fragments. This study demonstrates the possibility of convergence of next-generation sequencing technology and microchip oligonucleotides in terms of DNA synthesis cost reduction. In this study, however, high-throughput sequencing was carried out on chip oligonucleotides rather than on assembled DNA fragments. Accordingly, challenges associated with DNA assembly into larger sequences are still in early stages. Furthermore, an effective error-free oligonucleotide picking process necessitates a highly tuned bead picking robot and an image processing system.
A number of papers and patent publications are referenced and cited throughout the specification. The disclosures of the papers and patent publications are incorporated herein by reference in their entireties in order to more fully describe the state of the art to which the present disclosure pertains and the disclosure of the present disclosure.